Step 1: Buy a polarized replacement plug, if needed

Damaged plugs and nicked, frayed cords are a safety hazard
and need to be replaced. Putting a new plug on is
straightforward, but there are a few basic rules.

To prevent shocks from the metal parts of a light, lamp cords
and two-wire extension cords are always polarized. This means
the plug has a small blade for the hot wire and a wide blade for
the neutral wire, and the wires feeding those blades should not
be reversed when you put a new plug on. Always use a polarized
plug for a lamp, extension cord or any other cord that’s polarized
to begin with. Don’t ever use a nonpolarized replacement plug
with same-size blades to replace a polarized plug. (Nonpolarized
plugs are often found on double-insulated tools and some appliances.)

Step 2: Identify the neutral wire

You can identify the neutral side of the wire just by looking for
markings on one of the wires. The most common identifier is
ribbing in the rubber insulation all along one edge, but it can
also be a white wire or a white stripe (photo below).

How to Identify the Neutral Wire

To identify the neutral wire look for the markings shown in the photos.

Step 3: Wire the new plug

Photo 1: Strip the insulation

Strip the insulation off the wire by cutting and pulling the
wire through the wire stripper.

Photo 2: Connect the wires

Wrap each wire around the correct screw in a clockwise
direction, then screw it tight.

To prepare the cut end for a new plug, cut or pull the two sides
apart, then strip off about 3/4 in. of insulation (Photo 1). Lamp
and extension cords are usually 18 gauge, but if you’re not sure,
strip the wire through the 14- or 16-gauge slot first. If it doesn’t
strip cleanly, try the next gauge. Note: Stranded (“STRD”) wire
gauges are marked on the left, solid gauges are marked on the
right.

Twist the strands of wire tight, then fasten them into the
replacement plug with the neutral on the wide-blade side
(Photo 2). Then snap or screw the plug back together.